The present invention relates generally to a variable speed gearing system and, more particularly, to a mechanism for suppressing or reducing shocks (gear shift shocks) or vibrations/jars (gear shift judders) which may occur upon gear shifts.
Variable speed gearings designed to change the transmission gear ratios by engagement/disengagement of clutches have hitherto been known. Japanese Patent Laid-open Pub. No. Hei 6-505082 discloses by way of example a variable speed gearing of the type in which the clutches are engaged or disengaged by thrust forces applied to centrifugal clutches and planetary gears.
In the case of such clutches, the clutch engagement and disengagement are mechanically carried out, making it difficult to regulate and control the motions of the clutches, which often resulted in occurrence of gear shift shocks or judders upon gear shifting.
In the event of variable speed gearings which effect the gear shifts by the hydraulic drive of the clutches, a smooth clutch engagement/disengagement can be achieved by finely controlling the hydraulic pressure, although hydraulic pressure control means are necessitated resulting in a complicated structure.
It is an object of the present invention to provide a variable speed gearing system having a simple structure to reduce any shocks or judders which may be induced by gear shifts.
According to an aspect of the present invention, in order to attain the above object, there is provided a variable speed gearing system including two clutch units placed side by side in the axial direction, the variable speed gearing system providing a plurality of transmission gear ratios in response to the state of engagement of clutches of the two clutch units, the two clutch units being provided with axially movable members confronting each other; the variable speed gearing system comprising a piston member provided on one of the axially movable members confronting each other; and a cylinder member provided on the other of the axially movable members confronting each other, the piston member and the cylinder member constituting a damper mechanism in combination with each other.
Since the damper mechanism provides a resistance against the axial movements of the movable members upon the gear shifts depending on the rate of movements, it is possible to suppress any abrupt movement to ensure a smooth engagement and disengagement, to thereby reduce any possible gear shift shocks or gear shift judders.
Furthermore, the damper mechanism is constituted by the combination of the piston member and the cylinder member with utilization of the space defined between the two axially movable members confronting each other, whereby it is possible for the variable speed gearing system to have a simple configuration and reduced dimensions without any need to provide each clutch with a dedicated damper mechanism and without any need for a dedicated space therefor.
The variable speed gearing system may further comprise an oil chamber defined by the piston member and the cylinder member in cooperation, the oil chamber having an expanded or contracted volume; and communication passages extending from oil passages formed within shafts for axially movably supporting the movable members of the clutch units, into the oil chamber.
Thus, the oil chamber can be at all times fed with oil from the oil passage within the shaft through the communication passages, and the oil damper mechanism is implemented by the orifice effect of the communication passages allowing the oil to flow in and out due to the expansion and contraction of the oil chamber, whereby it is possible to achieve a smooth clutch engagement/disengagement to reduce the gear shift shocks or the gear shift judders.
The variable speed gearing system may further comprise flow control means disposed in the communication passages for imparting different passage areas to the communication passages between expansion and contraction of the oil chamber.
The relationships between the gear shift patterns and the magnitudes of the gear shift shocks will differ depending on the circumstances of use of the variable speed gearing system.
Thus, the flow control means provide a control so as to ensure that the passage areas of the communication passages become smaller upon the expansion if the gear shift patterns expected to present greater gear shift shocks occur upon the expansion of the oil chamber but that the passage areas become smaller upon the contraction if the gear shift patterns expected to present greater gear shift shocks occur upon the contraction of the oil chamber, whereby their resistances are increased so that the gear shift shocks can effectively be suppressed.